All-in-one liquid fert

Description

An all in one bottle bets that everything is short by the same amount. FAO's aquaponics manual, which is about plants grown in water fed by fish waste, does not describe a system that behaves that way. It splits plant nutrition into six macronutrients needed in relatively large amounts, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur, and a set of micronutrients needed only in traces, iron, manganese, boron, zinc, copper and molybdenum. All are essential. They are not equally likely to run out. The manual names the ones that actually go short in a fish fed system as potassium, calcium and iron, and says of magnesium that although its concentration is sometimes low it does not appear to be limiting and adding it is generally unnecessary. Its instruction when growth stalls is to identify which element is missing and correct that one, which is why it prints the deficiency signatures. Nitrogen shows as yellowing of older leaves with thin stems and poor vigour, because the plant pulls nitrogen out of old growth to feed new. Calcium shows in the newest growth instead, distorted, with hooked tips, because calcium cannot be moved once it has been placed. Iron shows as yellowing between the veins on new leaves. Where the symptom appears is half the diagnosis. Under all of it sits a trap. The manual's chapter on plants opens on pH rather than on nutrients, because pH governs access rather than supply. Outside roughly 5.5 to 7.5 plants hit nutrient lockout, where the nutrients are in the water and the plant cannot take them up, and FAO says that is especially true of iron, calcium and magnesium. Apparent deficiencies sometimes mean the pH is wrong. Dosing harder is then the wrong response, and no bottle on a shelf can tell you which case you are in.

Source

• openknowledge.fao.org — https://openknowledge.fao.org/items/e4d11efd-d97a-4959-8ae2-8b7d3fd32c5e

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